In the production of chipboard and fiber panels there is a requirement for precompression of the blanks by continuously working prepresses. Twin-belt presses in which the particle mat ("cake") of chips mixed with bonding glue deposited on a support is pulled off from the support before it enters the two forming belts of the press are known per se in the continuous production of wooden chipboard with precompression (DE 4441017 A1).
In other systems, on the other hand, known as "FLEXOPLAN" systems, the particle mat is formed by scattering the "glued chips" onto a flexible metal support screen on which they remain during precompression. At the head end of the support screen, a catch strip member is attached, 25 mm high, for example, which is engaged by chains that draw the support screen to the press. In these systems, it has not been possible to date to use a continuously working prepress because, in the passage of the catch strip member through the roller pairs and pressing segments of the known twin-belt presses, an inadmissibly high pressing pressure results and damages the forming belts and/or other parts of the press.
Systems in use to date do not allow continuous precompression of the panel material before hot pressing. Therefore, it has been necessary to provide a relatively large press plate spacing of about 25 cm, into which the chipboard cake was fed and then pressed relatively slowly, so that air can escape from the material. Precompressed panels are much thinner, so that a press plate spacing of 15 cm is sufficient and, for a press of the same height, it is possible to arrange 15 units one above the other instead of only ten with a larger plate spacing. Continuous precompression of the panel material is consequently very desirable. Not only because of the greater capacity of the hot press, but also because of the shorter pressing time since the precompressed material can also be pressed faster as a result of the smaller air content. In this way, productivity can be increased by about 50%.